The hydraulic pressure in the microcirculation of the rabbit omentum will be measured by means of the pressure servo nulling method in a microvascular network that exhibits vasomotor activity. Pressure measurements will be carried out downstream from the active arteriole, and in the capillaries and venules that originate from this vessel. Red blood cell flow velocity will be measured in the nailfold capillaries by means of video microscopy, with the objective of quantitating the various features of the vasomotor cycle in terms of flow. The rate at which a systemically injected dose of FITC Dextran with molecular weight ranging from 10 to 150,000 extravasates in the microcirculation will be measured by low light video densitometry. The objective of these studies is to characterize structural, geographical and temporal inhomogeneities in microvascular function which need to be considered when attempting to compare whole organ data with locally obtained microscopic data.